Myriotrochus hesperides O’Loughin & Manjón-Cabeza, 2009

O’Loughlin, Mark, Manjón-Cabeza, Eugenia & Ruiz, Francina Moya, 2009, Antarctic holothuroids from the Bellingshausen Sea, with descriptions of new species (Echinodermata: Holothuroidea), Zootaxa 2016, pp. 1-16 : 9

Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov.

Figure 2 e, f: table 1.

Material studied. Holotype. Antarctic Peninsula, BENTART–2006, R/V Hesperides , stn PA41, 65.47149ºS, 69.0285ºW, 350 m, 10 Feb 2006, MNCN 29.04/130; posterior dorsal body ossicles slide NMV F161516.

Diagnosis. Specimen 13 mm long; thin translucent body wall; sub-cylindrical, dorsal oral ring projecting anteriorly over ventral, body rounded distally; 12 peltato-digitate tentacles, each tentacle with about 7 small rounded digits; plates of calcareous ring asymmetrical, with short pointed anterior projections, wide rounded tongue-like posterior projections of variable length, 2 radial plates each with 2 anterior projections.

Tentacles lacking ossicles; body wall ossicles a few wheels only in the posterior dorsal body wall; wheels of one type, with teeth all pointing towards centre of hub; spokes irregular, about half branching proximally, some branches not reaching rim, some spokes with cross-connections; teeth variably sub-equal or different in size; hubs small, irregular, not disc-like, lacking perforations, formed by junction of spokes; largest wheel with diameter 248 µ m, hub diameter 40 µ m, 13 spokes at hub, 23 spokes at rim, 30 equal teeth; smallest wheel with diameter 200 µ m, hub diameter 24 µ m, 12 spokes at hub, 16 spokes at rim, 28 unequal teeth.

Colour (preserved). Off-white, translucent; tentacle digit ends reddish-brown.

Distribution. Antarctic Peninsula, 350 m.

Etymology. Named, as a noun in apposition, for the Spanish R/V Hesperides used for BENTART–2003 and BENTART–2006.

Remarks. Based on the key to the genera of family Myriotrochidae in Gage & Billett (1986), this new myriotrochid species is referred to Myriotrochus Steenstrup because it has: 12 tentacles; asymmetrical calcareous ring, with 2 radial plates each with 2 anterior projections; absence of rod ossicles; wheel hubs lacking perforations; wheel ossicles of one type only, with all teeth pointed towards centre of hub.

Three specimens of myriotrochid holothuroid have been taken in Antarctica . Smirnov and Bardsley (1997) described Myriotrochus antarcticus from a 2 mm long specimen from the MacRobertson Shelf in eastern Antarctica at 113 m. The wheels are 140–150 µ m in diameter, have 22–24 teeth, and 15–16 unbranched spokes, different to Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. A New Zealand National Institute of Water and Atmospheric Research (NIWA) single specimen of a Myriotrochus species (registration NIWA 37812, two pieces, combined length 33 mm) was taken in the Ross Sea at 2283 m in 2008. The wheel diameters are 320–395 µ m, have about 30 teeth, have 11–15 unbranched spokes and a perforated spoked hub, also different to Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. that is characterised by wheels with a small unperforated hub and frequently proximally branched spokes. The single type specimen is damaged, but appears to be intact, and has a complete oral end.

Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. has some characters that are similar to Myriotrochus clarki Gage & Billett, 1986 from the Rockall Trough in the NE Atlantic at 1605–2515 m. Both species have large tongue-like posterior projections on the calcareous ring, but these are larger in M. hesperides and the anterior projections smaller. An “abnormal” wheel with a few distally branched spokes is illustrated for M. clarki , but all the M. hesperides wheels have numerous proximally branched spokes.

Figures

FIGURE 2. a – c, Psolicrux iuvenilesi O’Loughin & Manjón-Cabeza sp. nov.: a, holotype (MNCN 20.04 / 128), lateral view, radial (left) and interradial plates of the calcareous ring (insert); b, spired plates (slide F 161523 from holotype) and spire from body wall (slide from specimen F 68053); c, tentacle ossicles (slide from specimen F 68053). d, Psolicrux coatsi (Vaney, 1908): tentacle ossicles (slide from specimen F 160026). e, f, Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov.: e, holotype (MNCN 29.04 / 130), oral end with calcareous ring left, asymmetrical plates of calcareous ring (insert); f, wheels from posterior dorsal body wall (slide F 161516).